The invention relates to a process for producing gas containing CO and H.sub.2 from pulverulent to coarse-grained coal in a fluidized bed of a gasifier, to which coal and exothermically reacting gasification agents are supplied through various inlets in the gasifier. The invention also relates to an apparatus for performing the process.
A number of different processes are known for producing gases containing CO and H.sub.2. In the so-called high temperature Winkler (HTW) process, preferably brown coal is brought to the gasifier pressure by means of a lock system and is then introduced into the lower part of the gasifier where it undergoes gasification. The disadvantage of this process is that gasification takes place at relatively low temperatures and the coal ash is discharged dry. As a result the production of CO and H.sub.2 in the gas produced is not generally high enough to permit the further use of the gas without subsequent treatment. In addition, casing and agglomerations of the pasty ash particles occur and there are problems when discharging the ash. The process is mainly intended for highly volatile, highly reactive coals, the coal conversion dropping considerably in the case of low volatility coals.
In the so-called Shell-Koppers process, there is an autothermic gasification of coal dust with oxygen or air and water vapor. The coal dust and gasification agents are introduced into the reactor in counter-current. Gasification takes place under pressure and under slagging conditions. Temperatures above 1400.degree. C. and pressures in the range 20 to 40 bar are sought.
It is disadvantageous that the coal must be ground into powdered form and consequently additional costs are incurred. It has also proved very difficult to dose the coal, because in this process it is necessary to stoichiometrically add coal and oxygen in order to achieve an optimum gas quality and a high carbon conversion.
DE-OS No. 27 50 725 discloses a process for producing a substantially CO and H.sub.2 -containing gas by gasifying aronaceous fuels in a melt, in which introduction takes place of the fuel and at least one oxidizing gasification agent. In this process, the fuel cannot be fed into the melt in the coarse-grained state and instead requires grinding. With respect to the stoichiometric addition, this process leads to the same disadvantages as in the Shell-Koppers process. The process is also limited to the use of low volatility coals, because otherwise there would be excessive spattering or an excessive temperature drop in the melt.
Finally, German patent 1 017 314 discloses a process for producing combustible gases, particularly synthesis gases, from pulverulent to coarse-grained fuels, in which the fuel layer is in an up an down whirling movement through the gasification agents and the gasification residues are removed in liquid or molten form. The endothermically reacting gasification agents are introduced into the upper part of the gas producer fuel layer, while the exothermically reacting gasification agents are introduced into the lower part thereof. The fresh fuel is either fed into the gas producer above the introduction point of the endothermically reacting gasification agents or between the introduction points of the exothermically and endothermically reacting gasification agents.
The use of different gasification agents and the supply of coal to the fluidized bed leads to considerable limitations with respect to the usability of the coal. If coal with a high proportion of volatile constituents and/or moisture is introduced, a relatively pronounced cooling takes place in the lower part of the gasifier, which impedes molten slag discharge. There is consequently a restriction to the use of certain high quality coal types. As a result of the supply of endothermic gasification agents, the gas produced has an excessive CO.sub.2 and possibly H.sub.2 O content for reduction purposes and e.g. the following composition is obtained: 10% CO.sub.2 ; 50% CO; 36% H.sub.2 ; 0.5% CH.sub.4 ; 3.5% N.sub.2.
On the basis of this prior art, the problem of the present invention is to provide a process for producing gas containing CO and H.sub.2 from pulverulent to coarse-grained coal with low proportions of CO.sub.2 and H.sub.2 O in a fluidized bed of a gasifier, to which coal and exothermically reacting gasification agents are supplied through different inlets in the gasifier, in such a way that the exothermically reacting gasification agents are substantially introduced into the lower part of the fluidized bed, which can be operated with pulverulent to coarse-grained coal of different qualities and in which there is a high thermal efficiency, whereby the slag can be removed in molten form.